1. Field of the Invention
The present invention relates to a method of measuring the distribution and intensity of ultrasonic waves used for ultrasonic diagnosis apparatuses and ultrasonic remedial apparatuses.
2. Prior Art
It is important to know the distribution and intensity of ultrasonic waves radiated by an ultrasonic diagnosis apparatus in studying the effect of the ultrasonic waves on an organism and in evaluating the ultrasonic diagnosis apparatus.
For an ultrasonic remedial apparatus, it is necessary to check the radiation characteristics of the remedial ultrasonic oscillation element because the radiation of ultrasonic waves must be concentrated in the direction of the diseased part. Further, even if the desired characteristics can be obtained at a particular frequency, those characteristics may change at another frequency. Therefore, one must have an understanding of the characteristics at varied frequencies.
Various methods of measuring the intensity and distribution of ultrasonic waves are conventionally known.
For example, an ultrasonic microphone is placed in a liquid in which ultrasonic waves are radiated and measured for intensity at the position where the microphone is placed. The distribution of the intensity can be also measured by changing the position of the ultrasonic microphone.
However, the measuring method utilizing an ultrasonic microphone has problems as described below. (1) Since an ultrasonic microphone having a certain volume is placed in the liquid, the presence of the ultrasonic microphone itself disturbs the distribution of the ultrasonic waves, thereby preventing accurate measurement of the distribution of the intensity. (2) Since an ultrasonic microphone generally has a narrow frequency band, it does not allow measurement of the intensity and distribution of ultrasonic waves in a wide frequency band. (3) In general, an ultrasonic microphone has directivity specific thereto. Therefore, the result of measurement varies depending on the orientation of the ultrasonic microphone. (4) The characteristics of the ultrasonic oscillation element can not be intuitively understood from the numerical data measured. This necessitates processes such as the graphing of the data. (5) Even if a graph is used, it is difficult to obtain three-dimensional representation of the intensity and distribution of ultrasonic waves. (6) Real time observation of three-dimensional changes in the intensity and distribution of ultrasonic waves is not possible.
In addition to the above described measuring method utilizing an ultrasonic microphone, there are well-known optical approaches such as the Schlieren method wherein changes in the refractive index due to radiation of ultrasonic waves are optically detected. Such optical approaches allow visualized measurement of the distribution of the sound field without disturbance to the state of the object to be measured caused by the measuring apparatus itself.
However, such optical approaches require a special light source and an imaging optical system such as a lens which make the measuring apparatus undesirably large.
There is another known method which utilizes the fact that application of ultrasonic waves to a certain substance causes the substance to emit a very small amount of light, i.e., the acoustic luminescence phenomenon, to measure three-dimensional distribution of the ultrasonic waves by way of photographs with long exposures. However, this method does not allow direct visualization and requires the photographic and development processes, which means that the measurement takes longer than is desirable.
Under such circumstances, it is an object of the present invention to provide a method of measuring three-dimensional distribution of ultrasonic waves which allows simple real time measurement.